1. Field of the Invention
The present invention relates to dielectric ceramic compositions for temperature compensation and relates to monolithic ceramic components, such as monolithic ceramic capacitors and monolithic LC filters, using the dielectric ceramic compositions.
2. Description of the Related Art
Ceramic capacitors for temperature compensation have been widely used for tuning and resonance in various electronic devices. Requirements for such capacitors are that they be compact and have low dielectric loss and stable dielectric characteristics. Thus, dielectric ceramics are required to have large dielectric constants and small dielectric loss (high Q values) under at reduced size.
BaOxe2x80x94TiO2 dielectric ceramic compositions are disclosed as such dielectric ceramics (H. M. O""Brayan; J. Am. Ceram. Soc., 57, (1974), 450, and Japanese Examined Patent Application Publication No. 58-20905), and monolithic ceramic capacitors using these dielectric ceramic compositions are being used in practice. Since these dielectric ceramic compositions are sintered at high temperatures of 1,300xc2x0 C. to 1,400xc2x0 C., metals durable at high temperatures, such as palladium (Pd) and platinum (Pt) must be used as internal electrodes.
In recent years, dielectric ceramic compositions which can be sintered at low temperatures have been disclosed, for example, a dielectric ceramic composition composed of a BaOxe2x80x94TiO2xe2x80x94Nd2O3-based primary constituent and a PbOxe2x80x94ZnOxe2x80x94B2O3xe2x80x94Al2O3xe2x80x94SiO2 glass (Japanese Unexamined Patent Application Publication No. 5-234420); a dielectric ceramic composition composed of a BaOxe2x80x94TiO2xe2x80x94Nd2O3-based primary constituent and a PbOxe2x80x94V2O5xe2x80x94B2O3xe2x80x94SiO2 glass (Japanese Unexamined Patent Application Publication No. 8-239262); and a dielectric ceramic composition composed of a BaOxe2x80x94TiO2xe2x80x94Nd2O3xe2x80x94Sm2O3-based primary constituent and a PbOxe2x80x94ZnOxe2x80x94B2O3 glass having a softening point of 500xc2x0 C. or less (Japanese Unexamined Patent Application Publication No. 9-71462).
These dielectric ceramic compositions contain glasses containing lead oxide (PbO) to facilitate sintering at low temperatures. The lead oxide is highly volatile during sintering and results in variable lead oxide contents in the same lot or in different lots in glass production and sintering of ceramics. Thus, characteristics of the resulting ceramic compositions are variable.
As described in Japanese Unexamined Patent Application Publication No. 9-71462, most of lead-free glasses have softening points exceeding 500xc2x0 C. and are unsuitable for sintering at low temperatures.
Accordingly, it is an object of the present invention to provide a dielectric ceramic composition for temperature compensation which has a high specific dielectric constant and a high Q value, can be sintered at low temperatures, can produce sintered ceramic having stable characteristics, and has high reliability.
It is another object of the present invention to provide a monolithic ceramic component, such as monolithic ceramic capacitor or a monolithic LC filter, using the monolithic ceramic component.
According to a first aspect of the present invention, a dielectric ceramic composition comprises 100 parts by weight of a primary constituent, about 0.1 to 25 parts by weight of a first secondary constituent comprising a SiO2-based glass not containing lead oxide, and more than about 0.5 to about 20 parts by weight of a second secondary constituent comprising manganese oxide (MnO), wherein the primary constituent is represented by the formula x(Ba60Caxcex2Srxcex3)O-y[(TiO2)1xe2x88x92m(ZrO2)m]-zRe2O3 wherein x+y+z=100 on a molar basis, xcex1+xcex2+xcex3=1, 0xe2x89xa6xcex2+xcex3 less than 0.8, 0xe2x89xa6m less than 0.15, and Re is at least one rare earth element, and the mole fraction (x, y, z) of (Baxcex1Caxcex2Srxcex3)O, (TiO2)1xe2x88x92m(ZrO2)m, and Re2O3 lies within a range surrounded by point A (7, 85, 8), point B (7, 59, 34), point C (0, 59, 41) and point D (0, 85, 15) in a ternary diagram shown in FIG. 1 wherein the line AB is not included.
According to a second aspect of the present invention, a dielectric ceramic composition comprises 100 parts by weight of a primary constituent, about 0.1 to 25 parts by weight of a first secondary constituent comprising a SiO2-based glass not containing lead oxide, and more than about 1.5 to about 20 parts by weight of a second secondary constituent comprising manganese oxide (MnO), wherein the primary constituent is represented by the formula x(Baxcex1Caxcex2Srxcex3)O-y[(TiO2)1xe2x88x92m(ZrO2)m]-zRe2O3 wherein x+y+z=100 on a molar basis, xcex1+xcex2+xcex3=1, 0xe2x89xa6xcex2+xcex3 less than 0.8, 0xe2x89xa6m less than 0.15, and Re is at least one rare earth element, and the mole fraction (x, y, z) of (Baxcex1Caxcex2Srxcex3)O, (TiO2)1xe2x88x92m(ZrO2)m, and Re2O3 lies within a range surrounded by point Axe2x80x2 (10, 85, 5), point Bxe2x80x2 (10, 59, 31), point Cxe2x80x2 (7, 59, 34), and point Dxe2x80x2 (7, 85, 8) in a ternary diagram shown in FIG. 2 wherein the line AB is not included.
According to a third aspect of the present invention, a dielectric ceramic composition comprises 100 parts by weight of a primary constituent, about 0.1 to 25 parts by weight of a first secondary constituent comprising a SiO2-based glass not containing lead oxide, and more than about 3.0 to 20 parts by weight of a second secondary constituent comprising manganese oxide (MnO), wherein the primary constituent is represented by the formula x(Baxcex1Caxcex2Srxcex3)O-y[(TiO2)1xe2x88x92m(ZrO2)m]-zRe2O3 wherein x+y+z=100 on a molar basis, xcex1+xcex2+xcex3=1,0xe2x89xa6xcex2+xcex3 less than 0.8, 0xe2x89xa6m less than 0.15, and Re is at least one rare earth element, and the mole fraction (x, y, z) of (Baxcex1Caxcex2Srxcex3)O, (TiO2)1xe2x88x92m(ZrO2)m, and Re2O3 lies within a range surrounded by point Axe2x80x3 (30, 70, 0), point Bxe2x80x3 (30, 59, 11), point Cxe2x80x3 (10, 59, 31), point Dxe2x80x3 (10, 85, 5), and point Exe2x80x3 (15, 85, 0) in a ternary diagram shown in FIG. 3.
In the first to third aspects, the first secondary constituent preferably comprises a B2O3xe2x80x94SiO2-based glass not containing lead oxide.
In these aspects, the dielectric ceramic composition preferably further comprises about 10 parts by weight or less of copper oxide (CuO) as a third secondary constituent.
According to a fourth aspect, a monolithic ceramic component comprises a plurality of dielectric ceramic layers, internal electrodes formed among the dielectric ceramic layers, and external electrodes connected to the internal electrodes, wherein the dielectric ceramic layers comprise the dielectric ceramic composition according to any one of the first to third aspects, and the internal electrodes comprise one of Cu and Ag as a primary constituent.
Examples of the rare earth elements Re in the present invention include La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.
The dielectric ceramic composition in accordance with the present invention can be sintered at a temperature of 1,060xc2x0 C. or less, and has a specific dielectric constant of 30 or more in the first aspect, 50 or more in the second aspect, or 60 or more in the second aspect, a Q value of 1,000 or more at 1 MHZ, and a temperature coefficient of capacitance (TCC) of xc2x130 ppm/xc2x0 C. in the first aspect, xc2x160 ppm/xc2x0 C. in the second aspect, or xc2x1120 ppm/xc2x0 C. in the third aspect. Since the composition does not contain volatile lead oxide, characteristics of the dielectric ceramic composition are stabilized.
A monolithic ceramic component, such as a monolithic ceramic capacitor or a monolithic LC filter, including dielectric ceramic layers composed of the dielectric ceramic composition, exhibits high moisture resistance. Moreover, inexpensive electrode materials, such as copper and silver, can be used in the monolithic ceramic component of the present invention. Thus, the monolithic ceramic component can be produced at reduced material cost.